There is an urgent need for a new glucose sensor for use in diabetes that can be implanted in tissues for the long term. GlySens is developing an implantable electrochemical glucose sensor based on the immobilized enzymes glucose oxidase and catalase and potentiostatic oxygen sensors that could potentially meet this need. The implant includes the sensor, electronics and telemetry, antenna, and battery. Glucose signals are transmitted to an external receiver that will display the actual glucose value and function as a hypoglycemia alarm. A key determinant of the ultimate success of the sensor is the long-term stability and catalytic activity of the immobilized enzymes, which is the focus of this proposal. We have determined that a combination of diffusion-limited design of enzyme domains in the sensor membrane and further chemical stabilization of the enzymes will be needed. Our efforts will include modeling of reaction-diffusion-inactivation and the optimal ratio of the two enzymes, application and optimization of a novel polymer system, and accelerated enzyme lifetime testing. [unreadable] [unreadable]